The Collaborative International Dictionary of English v.0.48:

Irascible \I*ras"ci*ble\, a. [L. irascibilis, fr. irasci to be
   angry, ira anger: cf. F. irascible. See Ire.]
   Prone to anger; easily provoked or inflamed to anger;
   choleric; irritable; as, an irascible man; an irascible
   temper or mood. -- I*ras"ci*ble*ness, n. -- I*ras"ci*bly,
   adv.
   [1913 Webster]

WordNet (r) 3.0 (2006):

irascible
    adj 1: quickly aroused to anger; "a hotheaded commander" [syn:
           choleric, irascible, hotheaded, hot-tempered,
           quick-tempered, short-tempered]
    2: characterized by anger; "a choleric outburst"; "an irascible
       response" [syn: choleric, irascible]

Moby Thesaurus II by Grady Ward, 1.0:

56 Moby Thesaurus words for "irascible":
   agitable, bearish, bitchy, cankered, cantankerous, churlish,
   contrary, crabbed, cranky, cross, cross-grained, crusty, cussed,
   difficult, disagreeable, edgy, emotional, emotionally unstable,
   eruptive, excitable, explosive, feisty, fractious, froward,
   high-mettled, high-spirited, high-strung, highly emotional,
   huffish, huffy, inflammable, irritable, mean, mettlesome, nervous,
   ornery, perturbable, perverse, prickly, sensitive, skittish,
   snappish, spiteful, spleeny, splenetic, startlish, stuffy, sulky,
   sullen, testy, touchy, ugly, volcanic, waspish, wayward,
   wrongheaded